1. Field of Invention
The present invention relates to a method for fabricating a passivation layer on a metal pad. More particularly, the present invention relates to a method for fabricating a passivation layer on a metal pad in which the passivation layer protects the metal pad from damage.
2. Description of Related Art
In a conventional semiconductor manufacturing process metal pads are formed on a substrate; some metal pads are for wire bonding and others serve as a high reflectance material layer. After the metal pads are formed, a first silicon dioxide layer serving as a passivation layer is formed by high density plasma chemical vapor deposition to cover the metal pads, and a thickness of the first silicon dioxide layer is 5000 to 15000 .ANG.. A chemical mechanical polishing process is performed to reduce the thickness of the first silicon dioxide layer. After the chemical mechanical polishing process, the thickness of the first silicon dioxide layer is 1500 to 2000 .ANG.. Then, a portion of the first silicon dioxide layer is removed by dry etching to expose the metal pads, so that the residual first silicon dioxide layer remains only between the metal pads. A second silicon dioxide layer whose thickness is controlled precisely and a silicon nitride layer are formed in sequence over the substrate. After light passes through the second silicon dioxide layer and the silicon nitride layer, and is reflected from the metal pads serving as the high reflectance material layer, constructive interference is produced.
In the above process, a dishing effect occurs after the chemical mechanical polishing process and the first silicon dioxide layer is excessively removed during the dry etching process. As a result, the planarity of the semiconductor is poor. Furthermore, the surface of each of the metal pads is damaged during the dry etching process, so that reflectance of each of the metal pads is reduced.